The invention concerns liftable hatch covers for decks or tank cover structures, especially for covers over tanks in sewage treatment plants. In particular the invention encompasses a safety barrier or grate that cooperates with the hatch cover and prevents service personnel from falling through an open hatch of such a tank cover.
Tank covers, particularly for sewage treatment tanks, are shown in U.S. Pat. Nos. 6,151,835, 6,012,259 and 5,941,027 of Hallsten Corporation. The tank covers, as well as liftable hatches for incorporation in the tank covers, are typically formed of interconnected extruded aluminum components, as shown in each of the above-listed patents.
The prior Hallsten patents, especially U.S. Pat. No. 5,941,027, show tank access hatches that hinge back a full 180° when fully opened, and this can be achieved via a special hinge, essentially a “gear hinge”.
Such tank access covers, especially for sewage treatment tanks, are opened for several reasons: to enable a worker actually to enter the tank for servicing, or to extend a servicing implement into the tank; or simply to admit a flow of air into the tank for aeration, the air being drawn by a fan located elsewhere in or on the tank. The open hatches present a problem of a worker accidentally falling through the opening.
This problem of open hatches, whether over a hatch opening in a public sidewalk, a floor access hatch, or a roof access opening or skylight, has been addressed previously. For example, see the “Hatch Safety Net”, marketed by Safe Approach of Poland, Me., comprising a polyester net that attaches to hook anchors on an aluminum frame that supports a hinged, solid hatch cover. The safety net can be removed from the hook anchors for access into the space below. The hatch with safety net is described as capable of being retrofitted in floor access hatches, roof scuttles, automatic fire vents or skylights. Also, USF Fabrication of Hialeah, Fla. produces a sidewalk hatch with hatch panels hinged on a frame, and one or more safety grate sections separately hinged along an edge of the frame which is perpendicular to the hinged edges of the hatch covers. The apparatus is described as “Double Safety Grate” or “Hinged Hatch Safety Grate”. The hatch/grate apparatus is typically used for public sidewalk access openings.
Another safety grate product, called “RETROGRATE SERIES X”, is produced by Halliday Products Inc. of Orlando, Fla. An aluminum double-door hatch cover is combined with a grate just below the doors, the grate being swingable upwardly for full access into the space below. Like the previously described product, the grate is pivoted on an axis perpendicular to the pivot axes of the hatch covers themselves.
The above safety grate devices are not directed to tank covers in sewage treatment applications, nor do they exhibit the efficient construction, operation and safety features of the invention described below.